1. Field of the Invention
This invention relates to a vibration generator, and more particularly to a vibration generator, for a portable equipment, which is useful when embodied in a silent alerting device such as a small-size bell alarm.
2. Description of the Related Art
In the conventional silent alerting device such as a pager, a vibration generator is mounted in which a weight is attached to a driving shaft of a motor in a mass eccentric position. Having the weight mass eccentrically attached to the driving shaft of the motor, vibration will be generated when the motor is rotated, giving a calling indicator to a person carrying the alerting device. Therefore this silent alerting device has been widely used as a vibration generator for an equipment having a vibrator mechanism, such as a pager or a massage device.
Generally in a small-size motor for equipment control, for obtaining a large start torque, it is required that the inertial moment of a rotating portion is small. Consequently, attempts have been made to reduce the weight of a rotor and the radius of rotation. A cup-shape coreless motor satisfies the above requirement as it has no rotating iron core and hence the radius of a rotor (a cup with an armature coil wound around) is small. Further, the silent alerting device for a small-size pager requires a small-size and light-weight device which generates a vibration large enough to cause bodily sensation. Therefore in the silent altering device of a conventional pager, it is preferable to use a cup-type coreless motor.
In manufacturing the vibration generator of a pager motor, material is sintered into a weight shape using a mold and the sintered material is cooled, whereupon the driving shaft of the motor is forced into the driving-shaft insertion hole. At that time, a secondary process is necessary in order that the size of a core pin's bore defining the driving-shaft insertion hole should be equal to the diameter of the driving shaft of the motor. This secondary process is exemplified by cutting the inside wall of the bore to a required size using, for example, a reamer. In an alternative method, the driving shaft of the motor is inserted into a weight's bore larger than the diameter of the driving shaft, and then the bore is clenched with a pin stop and by punching.
However, with the conventional silent altering device using a cup-type coreless motor, the following problems have been experienced. First of all, because a pager is to be carried by the user in his/her pocket, a small-size and light-weight pager is preferred. However, as long as a rotating mechanism is absolutely essential, there exists a limit in reducing the size of a cup-type coreless motor. As it uses a battery, the conventional silent altering device should preferably be of a low-energy-consuming type. Nonetheless using a cup-type coreless motor results in a relatively large consumption of power. As a general characteristic, a d.c. motor needs a large starting current. For the latest pager batteries, air cells are widely used as they are advantageous from size and weight view points, but an air cell is poor in supplying a large current, so this restriction to the starting current causes a malfunction of the motor. With this type of motor, particularly mechanical losses which occur in the bearings, brushes, etc. are significantly large. Further, in the brush section, electromagnetic noise will develop due to sparks, and the brush will wear out sharply with only a short life. Since the weight is attached to the driving shaft of the motor in a mass-eccentric position, the direction of vibration is changing all times so that an effective warning is difficult to achieve.
Further, in the conventional vibration generator mechanism, for production of the weight it is very difficult to make a motor-driving-shaft insertion hole, i.e., a bore in the core pin, and precise forced insertion management is impossible and must rely on secondary machining by, for example, a reamer. According to the method of clenching the bore, partly since the size of core pin bore formed in the weight does not coincide with the diameter of the driving shaft of the motor, and partly since the weight is fixed to the driving shaft of the motor by clenching, the driving shaft tends to be curved due to the clenching force so that the motor will suffer destructive damage. By the way, in the method of forming the vibration generator of the conventional pager motor, it is impossible to form the bore to an accurate size solely by primary machining, which requires some secondary machining, thus causing a poor rate of production and hence a high manufacturing cost.
There also exists a type of vibration generator where the movable member is supported by two or more leaf springs on either side of the coil. This technology, however, has the disadvantage that a large component of the vibration is non-linear. This non-linear motion component causes stress within the spring components and considerable friction between mechanical parts, thereby reducing operating life and reliability. In conventional alert systems of this type, this extra motion component is limited by pins or supports, which results in increased friction and power consumption, or by increasing the space between the movable member and coil, thereby increasing the size of the device and decreasing its unity.